Displacement pump and control system

ABSTRACT

A pump system includes a positive displacement pump, such as a diaphragm pump, an electric motor directly coupled to the positive displacement pump, and a programmable controller configured to maintain a desired current to the electric motor. The programmable controller is adapted to sense the current to the motor and to maintain constant current. It has been found that constant current provides constant torque and constant torque achieves constant fluid discharge pressure from the pump. The programmable controller utilizes an absorbed power formula to determine the correct current to achieve the necessary torque for a desired fluid discharge pressure. The programmable controller includes a power saving mode with minimal current and the pump is “dead headed” with no flow. The system is operated with a method that maintains constant fluid discharge pressure as well as having a power saving mode.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention is directed to a control system for pumps and in particular to a control system to a controller using current to maintain a constant fluid pressure.

Description of the Prior Art

Diaphragm pumps are used for a variety of purposes and applications and often require maintaining constant fluid pressure even under varying load conditions. Diaphragm pumps generally include a diaphragm, a pumping chamber, and a piston acting on hydraulic fluid on a first side of the diaphragm and separated from the pumping chamber by the diaphragm. The piston assembly is adapted to reciprocate and move between a first position and a second position to actuate the diaphragm. As the piston moves away from the diaphragm, the diaphragm flexes away from the pumping chamber allowing the pumping fluid to be drawn into the pumping chamber through an inlet passage. As the piston moves towards the diaphragm, the diaphragm flexes toward the pumping chamber and causes the fluid of the pumping chamber to be discharged through a discharge passage.

Often, such pumps are operated to maintain a constant fluid pressure. To control the fluid pressure even as the load changes, it is necessary to increase or decrease the pump speed. Generally controlling of the pump requires pressure sensors to provide feedback to increase or decrease the pumped fluid being discharged to maintain a fluid discharge pressure as pumping conditions may vary. Moreover, it can be appreciated that such controls typically require special connections, including wiring, as well as additional pressure sensors and may include a complicated controller with formulas to control the pump speed. Moreover, it may be difficult or even impossible to retrofit an existing pump so that it can achieve such constant fluid discharge pressure.

It can be seen then that a new and improved pump control system is needed. Such a system should control a pump to maintain a constant fluid pressure even under varying load conditions. Moreover, such a system should be reliable, simple and inexpensive. Such a system should be easy to adapt to existing installations without special fittings or attachment. The present invention addresses these, as well as others associated with pumps, pump control systems and maintaining constant fluid pressure.

SUMMARY OF THE INVENTION

The present invention is directed to a pump system includes a positive displacement pump, such as a diaphragm pump, an electric motor directly coupled to the positive displacement pump, and a programmable controller configured to maintain a desired current to the electric motor. The programmable controller is adapted to sense the current to the motor and to maintain constant current. The controller may be a variable frequency drive controller. It has been found that constant current provides constant torque and constant torque achieves constant fluid discharge pressure from the pump. The programmable controller utilizes an absorbed power formula to determine the correct current to achieve the necessary torque for a desired fluid discharge pressure. The programmable controller includes a power saving mode with minimal current and the pump is “dead headed” with no flow. When demand resumes from the power saving mode, the programmable controller detects acceleration from the power saving mode and is operably configured to apply the desired current. The system is configured for connecting to an external application solely with a current connection to the motor and a fluid connection to the pump.

A method for controlling the system includes programming the controller to control the system in a power saving mode with minimum current and torque with the pump having no flow. Using an absorbed power formula and setting a desired pump fluid discharge pressure, the current and torque requirements for the desired constant fluid pressure are determined. The controller then provides constant current to the motor corresponding to the torque for the desired constant fluid pressure. The controller maintains the current for the corresponding torque and fluid discharge pressure. The controller may be programmed to return the system to a power saving mode when demand ends. Moreover, as the torque automatically accelerates from the power saving mode when there is demand on the pump, the programmable controller senses the acceleration and returns to the current for the desired constant fluid discharge pressure.

These features of novelty and various other advantages that characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings that form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, wherein like reference letters and numerals indicate corresponding structure throughout the several views:

FIG. 1 is a perspective view of a pump, motor and control system according to the principles of the present invention;

FIG. 2 is a flow diagram for operating the system shown in FIG. 1;

FIG. 3 is a side sectional view of a diaphragm pump for the system shown in FIG. 1; and

FIG. 4 is a graph of torque versus current.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings and in particular to FIG. 1, there is shown a pump, drive and control system, generally designated (10). The system (10) includes a positive displacement pump, such as a diaphragm pump (20). The pump is driven by an electric motor (12). An inverter (14) with a programmable logic controller (16) provides overall control of the system (10). The controller (16) may be a variable frequency drive controller. It can be appreciated that the system (10) is particularly suited for providing and maintaining constant fluid pressure.

It can also be appreciated that the components have a modular configuration and may be adapted to a larger fluid system and provides “plug and play” connections with such connections only needed for power for the motor (12) and liquid for the pump (20). Therefore, the system (10) of the present invention is easily adapted and retrofitted to existing systems. It can also be appreciated that the motor (12) may include forced cooling for advantageous operation. The system may be adapted to multiple different systems such as providing constant pressure for tools without requiring special modifications to the system receiving the pumped fluid.

Referring now to FIG. 3, there is shown a positive displacement fluid pump such as a hydraulically driven diaphragm pump, generally designated (20). The diaphragm pump (20) is driven by a crankshaft (36) mounted in a crankcase (22). The manifold (26) includes an inlet passage (76) and a discharge passage (74). The manifold (26) also includes one or more inlet check valves (72) and one or more discharge check valves (70).

In the embodiment shown, the pump (20) is a diaphragm pump and includes a diaphragm (46) mounted on a valve stem (44). The diaphragm pump (20) may be a metering pump with very low flows that requires reliable precision inlet and discharge valves to achieve precise flow rates. However, it can be appreciated that the present invention is usable with many different types of pumps that use check valves. The diaphragm (46) is hydraulically driven by a plunger (42) connected to a slider (40) on connecting rod (38) to the crankshaft (36). The diaphragm system includes an overfill check valve (48) and an underfill check valve (50).

The diaphragm (46) receives fluid in a pumping chamber (34) and the fluid is pumped while the diaphragm deflects back and forth between an extended position and a fully retracted position. The manifold (26) includes separate inlet check valves (72) and discharge check valves (70).

Referring to FIG. 4, the torque at the pump shaft is controlled by motor current. Absorbed power formulas are utilized to measure the torque in relation to different electric currents. It has been found that the torque is directly proportional to the discharge pressure. Therefore, as torque is also linearly proportional to current, simple and reliable control is attained by providing a constant current to the motor (12), constant discharge fluid pressure may be achieved.

Referring to FIG. 2, achieving a constant discharge pressure may begin with the pump in a “dead headed” operating state. In such a mode, there is only a very small current provided and it is envisioned that the system (10) will require only 150 watts in this mode. To achieve a constant fluid discharge pressure, the torque required and therefore the current required is calculated. After these parameters are input, the controller (16) applies the current to the motor (12) to drive the pump (20) at the desired torque to achieve the constant discharge fluid pressure. The logic controller (16) then maintains the proper current to achieve the fluid pressure. When pumping operation is over, the programmable controller (16) again decreases the current so that a very slight trickle current is utilized.

The present invention utilizes direct drive of the motor (12) to the pump (20) without a gearbox. Moreover, no pressure sensors are required after initial parameters and relationships are determined. The constant fluid pressure is maintained with simple operation of the programmable logic controller (12).

It can be appreciated that the programmable logic controller (12) also provides for a metering/dosing control with different control software. The logic controller (12) is able to operate with the pump (20) dead headed, in which there is no flow, and is able to enter the sleep or power saving mode where current is reduced to a bare minimum for energy savings. Moreover, it can be appreciated that when there is flow demand, the minimal torque causes an acceleration, which is automatically detected and torque is therefore again applied at the desired level by the controller (16). The controller (16) generally utilizes an absorbed power formula to set and maintain the motor (12) to drive the pump (20) to achieve the desired flow rate.

It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

What is claimed is:
 1. A pump system, comprising: a positive displacement pump; an electric motor directly coupled to the positive displacement pump; and a programmable controller configured to maintain a desired current to the electric motor.
 2. The pump system according to claim 1, wherein the programmable controller comprises a current sensor.
 3. The pump system according to claim 1, wherein the positive displacement pump comprises a diaphragm pump.
 4. The pump system according to claim 1, wherein the programmable controller controls current according to an absorbed power formula.
 5. The pump system according to claim 1, wherein the programmable controller comprises a power saving mode.
 6. The pump system according to claim 5, wherein the programmable controller detects acceleration from the power saving mode and is operably configured to apply the desired current.
 7. The pump system according to claim 1, wherein the controller comprises a variable frequency drive controller.
 8. The pump system according to claim 1, wherein the system is configured for connecting to an fluid system solely with a current connection to the motor and a fluid connection to the pump.
 9. A method for controlling a positive displacement pump with a system including an electric motor and a programmable controller to achieve a desired constant fluid discharge pressure, the method comprising: programming the controller to control the system in a power saving mode with minimum current and torque with the pump having no flow; determining current and torque requirements for the desired constant fluid pressure; providing constant current to the motor corresponding to a torque for the desired constant fluid pressure; maintaining the current for the corresponding torque and fluid discharge pressure.
 10. The method according to claim 8, further comprising returning the system to a power saving mode when demand ends.
 11. The method according to claim 8, wherein the torque automatically accelerates when there is demand on the pump and wherein the programmable controller senses the acceleration and returns to the current for the desired constant fluid discharge pressure. 